1. Field of the invention
The present invention relates to map display systems and more particularly to map display systems so designed that a display is made by reading the desired map data from a recording medium preliminarily storing the map data of a whole area to be displayed.
2. Description of the Prior Art
Various map display apparatuses of the type employing a CRT or the like to display a road map, for example, have been proposed in the past. One such apparatus is designed so that the map data of a whole area to be displayed is preliminarily recorded in a map data recording medium including a magnetic tape, magnetic disc, CD ROM or the like, and the map data of the desired display district is read from the map data recording medium thereby displaying the desired map or district information on a CRT.
With this type of map display apparatus, it has been common to have the map data of a whole area to be displayed divided into a given number of sections and stored as such in a map data recording medium whereby the desired map data (section information) of the section to be displayed is extracted from the stored data and displayed on a CRT. Thus, there is a disadvantage that since the divided section information are simply recorded in order from the north to the south (or from the east to the west), even the sections adjoinging on the map are separately located on the map data recording medium. Thus, when displaying the map on the CRT or changing the displayed map, it is necessary to sequentially search the map data recording medium from the beginning and extract the desired section information thus requiring a considerable amount of time to read the map data.